1. Field of the Invention
This invention relates to an apparatus for processing of television camera signals used in close circuit television for recording and monitoring system.
2. Description of the Prior Art
In a monitoring television system used, as one of information transmission systems, at least one television monitor and one video cassette recorder are connected through an electronic switch to a plurality of television cameras and a plurality of transmission lines. The electronic switch provides selection of any one of the television cameras or sequential switching for displaying on the television monitor and recording into the video recorder a picture image of one camera after another.
In such an information transmission system, it is preferable to mutually lock the internal synchronizing signals of a plurality of television cameras and the electronic switching time to an external synchronizing signal, in order to prevent the picture image on the monitor from being disturbed during and immediately after the switching operation from one television camera to another.
As one of the devices for synchronizing a plurality of television cameras, there are known apparatus for transmitting vertical synchronizing signal and a horizontal synchronizing signal or composite synchronizing signal used in a television system. Another known apparatus for transmitting a vertical drive signal and a horizontal drive signal, and driving the television camera and its deflection circuits by the transmitted vertical drive signal, and the horizontal drive signal.
In any of the above known devices of the type under discussion, as the transmitted synchronizing signal itself is a train of pulses, which can be easily influenced by noise, the transmission of a synchronizing signal requires the use of a coaxial cable with its high shielding effect, which makes it costly for systems with plurality of television cameras.
Another known apparatus for synchronizing a plurality of television cameras, is an apparatus for transmitting an external synchronizing signal from an external synchronizing generator to the television cameras by injecting the external synchronizing signal into the video signal transmission line and locking an internal synchronizing signal generator of the television camera by means of the transmitted external synchronizing signal. Such an apparatus is disclosed in U.S. Pat. No. 4,603,352 the contents of which are incorporated herein by reference.
Furthermore, in such an information system, the switching rate from one camera to another must be slow in order to allow the supervisor time to observe the image on the monitor during the video recorder playback of the sequencing cameras. Therefore, the number of cameras in such a system is limited to a few only. If large number of cameras are used in such system, long period of time will elapse before all the cameras are recorded or played back in sequence which is laborious and inefficient.
In another known method for recording a plurality of images from plurality of television cameras, is by providing several video recorders to record the plurality of television cameras simultaneously, which is also laborious, and moreover, it is costly.